Gas or oil fired heat exchanger for forced air heating unit

ABSTRACT

A heat exchanger is shown having an elongated combustion chamber with a burner opening in one end thereof and a pair of ducts leading from the other end to a pair of separate headers. Two groups of tubes extend from the two headers along the combustion chamber for connection with a common header, and a third group of tubes extend back from the common header to a combustion gas discharge header positioned between the first two headers, but separate therefrom.

[ 1 Jan.23, 1973 United States Patent Nelson 3,028,854 4/1962 Reilly...................,........126/104 A X 3,053,246 9/1962 Kosan'n et a1.....................126/1l0 B GAS OR OIL FIRED HEAT EXCHANGER FOR FORCED AIR HEATING UNIT FOREIGN PATENTS OR APPLICATIONS 929,987 6/1963 Great Britain .................,..126/110 B [75] Inventor: Charles E. Nelson, Excelsior, Minn.

Primary Examiner-Char1es J. Myhre Attorney-Merchant & Gould [22] Filed:

[57] ABSTRACT A heat exchanger is shown having an elongated combustion chambers with a burner opening in one end thereof and a pair of ducts leading from the other end to a pair of separate headers. Two groups of tubes ex- [58] Field of Search.....l26/1 10 R, 119 B, 194 R, 1o4

tend from the two headers along the combustion chamber for connection with a common header, and a References Cited third group of tubes extend back from the common header to a combustion gas discharge header positioned between the first two headers, but separate therefrom.

UNITED STATES PATENTS 126/1103 ...126/ll0B 7 Claims, 6 Drawing Figures PATENTEU JAN 23 I973 SHEET 1 OF 2 INVENTOR. CHARLES E NELSON BY v a//fl4 r a am 0 A T TOFPN E Y5 PATENTEDJAHZIBISYS 3,712,286

INVENTOR. CHARLES E! NELSON ecwwvr 60am A T TO R N E Y5 GAS OR OIL FIRED HEAT EXCIIANGER FOR FORCED AIR HEATING UNIT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to heat exchangers and more particularly relates to the unique design of a gas or oil fired heat exchanger for a forced air heating unit.

2. Description of the Prior Art Applicant has the problem of designing a heat exchanger for a rooftop air conditioning unit in which heat is transferred from a gas or oil burner to a stream of air flowing through the unit. For a number of reasons, prior designs did not appear to be satisfactory. The unit had to be capable of utilizing either a gas burner or an oil burner or to be easily converted from one to the other. In many prior art heat exchangers, expansion and contraction caused metal fatigue and premature failure. This also produced noise caused by rapid heating and cooling of the unit. This noise is especially undesirable in a rooftop unit because of the difficulty in dampening the noise. Another problem with many prior art heat exchangers is that they contain various internal baffles, flue restrictors, etc. intended to create certain air flow through the unit and to increase efficiency. However, it has been my experience that these devices tend to wear out and eventually drastically reduce efficiency. Also, prior art heat exchangers of two pass design created excessive heat release at the end opposite the burner causing unequal and stratified heating in downstream ducts.

SUMMARY OF THE INVENTION The heat exchanger of the present invention provides three passes of the heated combustion gases across the air flow path. Balanced heat released from end to end is thus achieved. Substantially all parts of the heat exchanger are in contact with both the internal flue gases and the external air so that virtually every piece of metal performs a heat exchanging function. The unit has no internal baffles, flue restrictors, swirlers, etc.

and as a result, the life expectancy of the unit is much longer than usual. The heat exchanger disclosed herein will accept either a gas or oil burner and can be easily converted from one to the other. The burner assembly and the heat exchanger unit are separately mounted to a common mounting plate such that one can be removed from the unit without disturbing the other. Another important feature of the present invention is. that the three groups of heating tubes are connected at one end to a common header but at the other end to separate headers so that different rates of tube expansion and contraction are accommodated. Noise has therefore been significantly reduced, as well as metal fatigue resulting from the expansion and contraction. As a result of these improvements, a more efficient heat exchanger has been provided, that is much quieter and that has a longer life expectancy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective of a rooftop air conditioning unit of the type in which the present heat exchanger is mounted;

FIG. 2 is an enlarged view, in perspective, of the heat exchanging unit mounted in the air conditioning unit of FIG. 1;

FIG. 3 is a view of the end of the heat exchanger opposite that shown in FIG. 2, portions thereof being broken away and portions being shown in section;

FIG. 4 is an enlarged sectional view of the air conditioning unit taken along line 4-4 of FIG. 1;

FIG. 5 is an enlarged fragmentary sectional view taken along line 5-5 of FIG. 4; and

FIG. 6 is a view in perspective of the common mounting frame for the heat exchanger unit and burner assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference numerals will be used throughout the several views to indicate like elements of the invention, there is disclosed an air conditioning unit 10 having a side wall 1 l with an access door 12 mounted therein by means of a hinge 13. Outside air enters the unit 10 through a set of dampers 14 in an end wall 15. Air conditioning unit 10 is mounted on a building roof 16 by means of a curbing 17 connected between the unit and the roof. A return air duct, not shown, enters the unit through the roof. Conditioned air leaves the unit 10 through a duct 20 that also extends downwardly through the roof 16. The opening 21 in side wall 11 is an outlet for combustion gases from the heat exchanger unit. This may have either a flue gas diffuser or flue pipe attached. The circular device 22 in side wall 11 is a viewing port for the gas or oil fired flame in the heat exchanger. Unit 10 is also provided with a sheet metal top cover 19 having a peripheral lip that overhangs the side and end walls.

FIG. 2 discloses a heat exchanger 23 which, as shown in FIG. 4, is mounted in air conditioning unit 10. Heat exchanger 23 includes an elongated combustion chamber 24 that is hexagonal in cross section. One end of chamber 24 is provided with a burner receiving opening 25 having connected to the periphery thereof a tubular extension member 26 having secured to its free end, perpendicular thereto, a rectangular metal mounting flange or plate 27. Extending outwardly from the face of flange 27, adjacent the corners thereof, are four threaded studs 28.

The viewing port 22 is situated in the other end of chamber 24. Being hexagonal, combustion chamber 25 has six outer and inner wall surfaces extending from end to end thereof. Extending laterally from two of the adjoining wall surfaces adjacent the end having the viewing port 22 are a pair of spaced ducts 29 and 30.

' Ducts 29 and 30 provide an outlet for the combustion gases being generated in chamber 24. Connected to the ends of ducts 29 and 30 are first and second spaced headers 31 and 32. The headers 31 and 32 are each formed as a rectangular box having access plates 31a and 32a bolted to the exterior walls thereof. Connected to the opposite walls of headers 31 and 32 are groups of tubes 33 that extend away therefrom generally parallel to combustion chamber 24. In the preferred embodiment, four tubes are connected to each of headers 31 and 32'. All of the tubes are of the same length and extend parallel to each other.

Connected to the other ends of the tubes 33 is a third common header 35 that is positioned adjacent the burner receiving end of the chamber 24. As best shown in FIG. 3, there are three groups of the tubes 33 and four tubes in each group. The number of tubes will obviously vary depending upon the capacity of the unit. However, in the preferred embodiment, there are four tubes extending between first header 31 and third header 35, and another four tubes extending between second header 32 and third header 35. A third group of four tubes 33 is connected to common header 35 between the first two groups, in parallel therewith. The other end of this third group of tubes 33 is connected to a fourth header 36 having a flue gas outlet 37 formed in the outer wall thereof. A mounting flange 38 is mounted around outlet 37 and is provided with a plurality of outwardly extending mounting studs 39. Fourth header 36 is connected only to the side wall 11 by studs 39 and to the ends of the associated tubes 33. It is not otherwise connected to headers 31 or 32, or to combustion chamber 24.

It can be seen that the gases being formed from combustion in chamber 24 leave the chamber through the two ducts 29 and 30 so that generally equal amounts of combustion gases are received by headers 31 and 32. The combustion gases leave the headers 31 and 32 through the associated tubes 33 and are discharged thereby into common header 35. The gases leave common header 35 through the four tubes 33 leading to fourth header 36 and are discharged from the unit through the outlet 37.

As best shown in FIG. 4, heat exchanger 23 is mounted in a plenum chamber 41 of the forced air heating unit or air conditioning unit such that air is forced over substantially the entire surface thereof. The heat exchanger 23 is positioned as shown in FIG. 3 so that air first passes over the combustion chamber 24 and then over the headers and tubes 33. A pair of legs 42 are connected between header 32 and a floor18 of the air conditioning unit. Another pair of legs 43 are connected between common header 35 and the floor 18. As best shown in FIG. 4, the threaded studs on flange 37 extend through side wall 11 and suitable nuts are threadedly secured thereto, to provide support for fourth header 36.

Air conditioning unit 10 is provided with a common support wall 45 positioned at one side of plenum chamber 41 opposite from side wall 11, and parallel thereto. As shown in FIG. 6, support wall 45 includes upper and lower horizontally extending frame members 46 and 47 and a pair of vertical, spaced frame members 48 and 49 connected therebetween. As shown in FlG. 4, inner and outer walls 45a and 45b are connected to this frame and an insulation material 450 is positioned in the voids between the two wall surfaces and frame members 46-47. Welded between the two vertical frame members 48 and 49 is a metal mounting plate 50 having openings 28a therein to receive the first group of studs 28 and a large, central burner receiving opening 50a. A group of threaded studs 51 extend outwardly therefrom, and are spaced closer to the burner receiving opening 50a than the stud receiving openings 28a. As best shown in FIGS. 4 and 5, a burner assembly 52 is bolted to the outwardly extending studs 51. so that the burner extends into extension member 26 and chamber 24. The studs 28 on mounting flange 27 extend through the openings 28a of mounting plate 50 and are secured thereto as shown in FIG. 5. The burner receiving end of combustion chamber 24 is thus supported by common 5 support wall 45. Because the mounting studs 28 and 51 are offset from each other, the heat exchanger unit 23 and the burner assembly 52 are separately demountable from support wall 45.

As best shown in FIG. 3, combustion chamber 24 is mounted so that its upper and lower wall surfaces are horizontal. Four elongated air deflecting vanes 54 are secured to chamber 24 by means of mounting brackets 55 welded thereto. The vanes 54 are mounted along and spaced from the entire length of the heat exchanger 24 at the opposite edges of the upper and lower horizontal wall surfaces thereof. Each of the vanes 54 comprise two flat portions 54a and 54b that form an obtuse angle with respect to each other, the angle corresponding generally to the angle between adjacent wall surfaces of the combustion chamber 24. Thus, one flat portion 54b is generally parallel to the horizontal wall surface of chamber 24, and the other flat portion 54a is generally parallel with the adjoining wall surface. The vanes 54 are designed to force a portion of the air entering the plenum chamber 41 to pass directly over the entire outer surface of combustion chamber 24 so that it is exposed to the entire heating surface thereof.

After the air passes over combustion chamber 24, as

guided by the vanes 54, it passes among the tubes 33 and around the headers 31, 32, and 36. All of these units transfer heat from the interior combustion gases to the air passing thereover. As previously mentioned, there are no interior baffles etc. within the combustion chamber, headers or tubes. A suitable back pressure is built up within the heat exchanger by virtue of the fact that only four tubes 33 are connected to the discharger header 36. This back pressure ensures that the gases are not discharged until they have surrendered a major portion of their heat.

Because various portions of the heat exchanger unit 23 are heated to different temperatures at different times, they expand and contract at different rates. The unit is designed to accommodate these expansions and contractions without undue stresses or noise occurring. For one thing, only one end of the combustion chamber 24 is connected to the header and tube assembly. Further, only one end of the combustion chamber 24 is directly connected to the walls of the air conditioning unit. Thus, combustion chamber 24 can freely expand with respect to the walls of the air conditioning unit and also with respect to the tube and header assembly. The headers at the discharge end of the unit are an especially critical area for expansion and contraction because the two outer groups of tubes operate at a different temperature from the inner group of tubes. To accommodate the different ratesof expansion and contraction of these groups of tubes, discharge header 36 is not connected to the other headers 31 and 32. This separate mounting of the discharge header 36 eliminates a major problem area with respect to both stresses and noise. It is noted that discharge header 36 is connected to side wall 11 but that header 35 is not connected to support wall 45. Although common header 35 is supported by legs 43 on floor 18, the legs are not connected to the floor, thereby permitting lateral movements of header 35 relative to floor 18, resulting from expansion and contraction of the tubes.

What is claimed is:

1. A heat exchanger for a forced air heating unit comprising:

a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof;

b. first and second spaced headers connected to said ducts;

c. a third header positioned adjacent said one end of said combustion chamber;

d. a fourth header having a flue gas outlet therein positioned between said first and second headers;

e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom; and

f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, the mounting means including a first plurality of mounting legs connected between a support surface of said unit and said second header, and a second plurality of mounting legs supporting said third header on said support surface so as to permit relative lateral movement therebetween, and further including said fourth header and said one end of said combustion chamber being connected to said unit.

2. A heat exchanger for a forced air heating unit comprising:

a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof;

b. first and second spaced headers connected to said ducts;

c. a third header positioned adjacent said one end of said combustion chamber;

d. a fourth header having a flue gas outlet therein positioned between said first and second headers;

e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom;

f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, with the air first passing over said combustion chamber and then over said headers and tubes; and

. elongated air deflecting vanes being mounted to the outer surface of said combustion chamber to direct the flow of air thereover.

3. The apparatus of claim 2 wherein said combustion chamber is hexagonal in cross section and is mounted to have horizontal, parallel upper and lower wall surfaces.

4. The apparatus of claim 3 wherein said vanes are mounted along and spaced from the length of said heat exchanger at edges of said upper and lower surfaces,

each of said vanes comprising two flat portions forming an obtuse angle with respect to each other, corresponding generally to the angle between adjacent wall surfaces of said combustion chamber.

5. A heat exchanger for a forced air heating unit comprising:

a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof;

b. first and second spaced headers connected to said ducts;

c. a third header positioned adjacent said one end of said combustion chamber;

(1. a fourth header having a flue gas outlet therein positioned between said first and second headers;

e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom;

f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, with the air first passing over said combustion chamber and then over said headers and tubes;

g. a metal mounting flange connected to the periphery of said burner receiving opening having a first group of threaded studs extending outwardly therefrom, a mounting plate supported by said unit having openings therein to receive said first group of studs, a central burner receiving opening and a second group of threaded studs extending outwardly therefrom spaced closer to said burner receiving opening than said first group, and a burner assembly mounted on said second group of studs opposite said mounting plate from said heat exchanger, said heat exchanger and said burner assembly thereby being separately demountable from said mounting plate.

6. A heat exchanger for a forced air heating unit comprising:

a. an elongated combustion chamber having a burner receiving opening in one end thereof and duct means leading from the other end thereof;

. first and second spaced headers connected to said duct means;

. a common header positioned adjacent said one end of said combustion chamber;

. a discharge header having a flue gas outlet therein positioned between said first and second headers;

. a plurality of tubes connected between said common header and said other headers to provide a combustion gas flow path; and

f. said common header and one of said first and second headers being supported by a support surface of said unit, said burner receiving opening end of said chamber being connected to a support wall of said unit, and said discharge header being secured to a side wall of said unit, to provide the entire support of said heat exchanger in a plenum chamber of said unit.

7. A heat exchanger for a forced air heating unit comprising:

7 8 a. an elongated combustion chamber havingaburner iv. a plurality of tubes connected between said receiving opening in one end thereof and a pair of third header and said other headers to provide a spaced ducts leading from the other end thereof; combustion gas fl h f id h mb and through said ducts into said first and second ahead and tube assembly compnsmg: headers, then through certain of said tubes to i. first and second spaced headers connected to said ducts, providing the sole connection between said combustion chamber and said header and tube assembly to permit different rates of expansion and contraction thereof; 10

ii. a third header positioned adjacent said one end of said combustion chamber;

said third header and then through the remaining tubes to said fourth header for discharge therefrom, said fourth header being connected to said header and tube assembly solely by said remaining tubes to thereby permit a different rate of expansion and contraction thereof with iii. a fourth header having a flue gas outlet therein respect to Said certain of Said tubes and Said first positioned between said first and second and Second headers headers; and 

1. A heat exchanger for a forced air heating unit comprising: a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof; b. first and second spaced headers connected to said ducts; c. a third header positioned adjacent said one end of said combustion chamber; d. a fourth header having a flue gas outlet therein positioned between said first and second headers; e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom; and f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, the mounting means including a first plurality of mounting legs connected between a support surface of said unit and said second header, and a second plurality of mounting legs supporting said third header on said support surface so as to permit relative lateral movement therebetween, and further including said fourth header and said one end of said combustion chamber being connected to said unit.
 2. A heat exchanger for a forced air heating unit comprising: a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof; b. first and second spaced headers connected to said ducts; c. a third header positioned adjacent said one end of said combustion chamber; d. a fourth header having a flue gas outlet therein positioned between said first and second headers; e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom; f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, with the air first passing over said combustion chamber and then over said headers and tubes; and g. elongated air deflecting vanes being mounted to the outer surface of said combustion chamber to direct the flow of air thereover.
 3. The apparatus of claim 2 wherein said combustion chamber is hexagonal in cross section and is mounted to have horizontal, parallel upper and lower wall surfaces.
 4. The apparatus of claim 3 wherein said vanes are mounted along and spaced from the length of said heat exchanger at edges of said upper and lower surfaces, each of said vanes comprising two flat portions forming an obtuse angle with respect to each other, corresponding generally to the angle between adjacent wall surfaces of said combustion chamber.
 5. A heat exchanger for a forced air heating unit comprising: a. an elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof; b. first and second spaced headers connected to said ducts; c. a third header positioned adjacent said one end of said combustion chamber; d. a fourth header having a flue gas outlet therein positioned between said first and second headers; e. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header, and then through the remaining tubes to said fourth header for discharge therefrom; f. said heat exchanger being mounted in a plenum chamber of a forced air heating unit for passage of air thereover, with the air first passing over said combustion chamber and then over said headers and tubes; g. a metal mounting flange connected to the periphery of said burner receiving opening having a first group of threaded studs extending outwardly therefrom, a mounting plate supported by said unit having openings therein to receive said first group of studs, a central burner receiving opening and a second group of threaded studs extending outwardly therefrom spaced closer to said burner receiving opening than said first group, and a burner assembly mounted on said second group of studs opposite said mounting plate from said heat exchanger, said heat exchanger and said burner assembly thereby being separately demountable from said mounting plate.
 6. A heat exchanger for a forced air heating unit comprising: a. an elongated combustion chamber having a burner receiving opening in one end thereof and duct means leading from the other end thereof; b. first and second spaced headers connected to said duct means; c. a common header positioned adjacent said one end of said combustion chamber; d. a discharge header having a flue gas outlet therein positioned between said first and second headers; e. a plurality of tubes connected between said common header and said other headers to provide a combustion gas flow path; and f. said common header and one of said first and second headers being supported by a support surface of said unit, said burner receiving opening end of said chamber being connected to a support wall of said unit, and said discharge header being secured to a side wall of said unit, to provide the entire support of said heat exchanger in a plenum chamber of said unit.
 7. A heat exchanger for a forced air heating unit comprising: a. An elongated combustion chamber having a burner receiving opening in one end thereof and a pair of spaced ducts leading from the other end thereof; and b. a header and tube assembly comprising: i. first and second spaced headers connected to said ducts, providing the sole connection between said combustion chamber and said header and tube assembly to permit different rates of expansion and contraction thereof; ii. a third header positioned adjacent said one end of said combustion chamber; iii. a fourth header having a flue gas outlet therein positioned between said first and second headers; and iv. a plurality of tubes connected between said third header and said other headers to provide a combustion gas flow path from said chamber through said ducts into said first and second headers, then through certain of said tubes to said third header and then through the remaining tubes to said fourth header for discharge therefrom, said fourth header being connected to said header and tube assembly solely by said remaining tubes to thereby permit a different rate of expansion and contraction thereof with respect to said certain of said tubes and said first and second headers. 